Solid free-flowing phosphonate composition and method of use

ABSTRACT

Solid free-flowing compositions of a magnesium salt of bis(hexamethylene)triamino penta(methylenephosphonic) acid are disclosed. The compositions exhibit desirable scale inhibitor properties and can be used in water treatment. In addition, a method of scale control is disclosed using the magnesium phosphonic acids under ambient conditions of relative humidity of at least 30% as can apply under subtropical or tropical conditions of high relative humidity. The preferred molar ratios of magnesium to phosphionic acid are in the range of from 1:1 to 3:1.

[0001] This invention relates to a solid free-flowing compositionconsisting essentially of a magnesium salt of bis(hexamethylene)triaminopenta(methylenephosphonic) acid, having a molar ratio of magnesium tophosphonic acid of from 1:1 to 5:1. The phosphonate magnesium saltexhibits scale inhibitor properties and the composition can be usedbeneficially in water treatment. In a preferred embodiment, theinvention contemplates a method of scale control under ambientconditions of relative humidity of at least 30% as can apply undersubtropical or tropical conditions of high relative humidity.

[0002] Organic phosphonates, including polyamino species, are old in theart and have been used in various applications such as industrial watertreatment, detergent and scale inhibition, particularly barium hardnesscontrol in connection with off shore marine oil drilling.Bis(hexamethylene)triamino pentamethylene phosphononic (BHMT) acid andcertain salts are known from U.S. Pat. No. 3,613,788. The structuralchemical formula of BHMT can be found in that US patent at the top ofcolumn 2. Shiliang He et al., Water Soluble Polymers, edited by Amjad,Plenum Press, New York 1998, pages 163-171, also relates to theinhibition of mineral scale precipitation by polymers. The polymers canbe represented by a large variety of species including polyacrylates andtheir derivatives and polyphosphonates including polyamino species suchas BHMT. Shiliang He et al., Langmuir 1996, 1901-1905 describe amathematical inhibitor model for barium sulfate scale control therebyreporting, in particular, the measured inhibition kinetics of bariumsulfate nucleation with BHMT and several other polyphosphonate andpolyacrylate inhibitors. Zieba A. et al., Langmuir 1996, 12, 2853-2858,have reported the influence of a series of organic polyphosphonates onhydroxyapatite crystal growth kinetics. U.S. Pat. No. 3,880,764discloses conventional polymer aqueous drilling fluid containing a scalecontrol additive which can be represented by BHMT.

[0003] BHMT has, notwithstanding a standing desire, never foundwidespread application in industrial water treatment and scale control.While it was known that di-long-alkyl triamino pentamethylenephosphonates showed superior stability under stress conditions includinghigher temperatures, pressure and humidity, as can e.g. apply in oildrilling application, such use, of the solid BHMT salt form, waspractically impossible, or non-economic due to the hygroscopicity of thealkali salts and the calcium salts. BHMT is normally used, and dependingupon the pH requirement, as a sodium salt, more exceptionally as acalcium salt. The BHMT deficiency was such that the known solid saltscould not be used as such.

[0004] It is a first object of this invention to provide solid dry formsof BHMT phosphonic acids for use in scale control application. It isanother object of this invention to provide solid BHMT sequestrantsand/or inhibitors capable of being used economically under humid and/oradverse ambient (subtropical/tropical) conditions as can apply.

[0005] It was now discovered that the foregoing and other objects ofthis invention can be met by using solid, free-flowing magnesium saltsof BHMT, preferably partial magnesium salts. In another aspect, thisinvention relates to a method of scale control under ambient conditionsof relative humidity of at least 30% wherein a solid free-flowingcomposition is used consisting essentially of a magnesium salt of BHMThaving a molar ratio of magnesium to phosphonic acid of from 1:1 to 3:1,preferably of from 1.9:1 to 2.8:1.

[0006] Percentages used in this description stand, unless indicatedotherwise, for percentage by weight. The term BHMT stands forbis(hexyl)triamino pentamethylene phosphonic acid. The term phosphonicacid, as used throughout the description and claims, in connection withmolar ratios refers obviously, and by proper antecedent, to BHMT.

[0007] The invention herein relates to solid free-flowing compositionscapable of exhibiting useful scale control properties consistingessentially of a magnesium salt of BHMT having a molar ratio ofmagnesium to phosphonic acid of from 1:1 to 5:1. In one preferredexecution, the magnesium salt of BHMT represents, at least, 70% of thecomposition. The invention also concerns a method of scale control underambient conditions of relative humidity of, at least, 30% characterizedin that one uses a solid free-flowing composition consisting essentiallyof a magnesium salt of BHMT having a preferred molar ratio of magnesiumto phosphonic acid in the range of from 1.9:1 to 2.8:1. More in general,the preferred molar ratios, in connection with the composition aspectsof the invention herein, of magnesium to phosphonic acid are generallywithin the range of from 1:1 to 3:1, preferably in the range of from1.5:1 to 2.5:1 most preferably of from 1.9:1 to 2.1:1. The partialmagnesium salts of BHMT, having e.g. a phosphonic acid/magnesium ratioas set forth in the preceding sentence, can depending upon the use pHrequirement of the solid free-flowing product be partially neutralizedwith alkali cations, preferably sodium, or other suitable neutralizingagents well-known in the art. In one execution, a preferred pH of thesolid free-flowing partial magnesium salt is in the range of from 6 to8, the pH being measured in a 1% by weight solution of the solid productin distilled water at 25° C. The BHMT salt can thus be represented by amagnesium salt having a molar ratio of magnesium to phosphonic acid of5:1 or by partial magnesium salts which are partially neutralized byother agents such as sodium hydroxide. Inasmuch as the pH of the solidfree-flowing magnesium salt shall preferably have a pH (1%; 25° C.) ofaround 6 to 9 it follows that the sodium ions can neutralize thenon-magnesium neutralized acid functions i.e. up to four sodiums withrespect to BHMT carrying three magnesiums. But the amount of sodium willvary depending upon the pH of the BHMT magnesium salt solution, which pHis frequently in the range of from 6 to 9. Such final pH optimizationsof the BHMT magnesium salt solutions are routine undertakings.

[0008] The compositions in accordance with the invention, which can alsobe used in the method embodiments of the invention, consist essentially,i.e. 50% or more, of the BHMT magnesium salt, preferably at least 70% ofthe BHMT magnesium salt. The compositions can, in addition, containminor levels of conventional additives producing, upon use in artestablished additive levels, a known functionality. Examples of the likeadditives include solid fillers and diluents, dyes, perfumes and alsoadditive levels, frequently below 30%, usually below 20%, of thecomposition, of conventional scale inhibitor compounds other than BHMT.Examples of such scale inhibitors which have been commonly used inindustrial treatment include polyacrylates and derivatives thereof andpolyphosphonates including hydroxyethylidene-1,1 diphosphosphonate,nitrilotrimethylenephosphonate, sulfonated polyacrylate andphosphinopolycarboxylate. The claimed composition and methodtechnologies can be used in industrial water treatment, detergent andscale inhibition, hardness control in oil drilling operations andparticularly in marine oil drilling as a means for controlling bariumhardness control. In the method aspect herein, the magnesium—BHMT saltis used in levels generally in the range of from 1 to 1000 ppm,preferably 2 to 300 ppm, more preferably 2 to 100 ppm.

[0009] The “70%” level of the BHMT magnesium salt refers to total activeBHMT salts in pH adjusted form and thus comprise BHMT and relative BHMTby-products i.e. expresses total active salts measured by acid-basetitration.

[0010] The hygroscopicity of a series of BHMT salts was compared at 30°C. under conditions of increasing relative humidity (RH); measurementswere effected after three hours of exposure. The testing results are asfollows: Salt pH RH % Remarks BHMT (N_(a))₇ 7 35 wet and sticky 45 syrup50 liquid 65 liquid BHMT (M_(g))₂ 7 35 free-flowing 45 free-flowing 65free-flowing BHMT M_(g) 7 35 free-flowing 45 traces of surface cakingBHMT (C_(a))_(2.5) 10 35 sticky and crusty

[0011] These results show the unusual retention of free-flowingproperties of magnesium salts having, for example, a molar ratio ofmagnesium to phosphonic acid above 1.5:1, preferably in the range offrom 2:1 to 3:1.

1. A free-flowing solid composition, capable of exhibiting scale controlproperties, consisting essentially of a magnesium salt ofbis(hexamethylene)triamino penta(methylenephosphonic acid), having amolar ratio of magnesium to phosphonic acid of from 1:1 to 5:1.
 2. Thecomposition according to claim 1 wherein the molar ratio of magnesium tophosphonic acid is in the range of from 1:1 to 3:1.
 3. The compositionaccording to claim 2 wherein the magnesium salt of the phosphonic acidrepresents, at least, 70% by weight of the composition.
 4. Thecomposition according to claim 3 wherein the molar ratio of magnesium tophosphonic acid is from 1.5:1 to 2.5:1.
 5. A method of scale controlunder ambient conditions relative humidity of at least 30% wherein oneuses a solution containing a free-flowing solid composition consistingessentially of a magnesium salt of bis(hexalmethylene)triaminopentamethylene phosphonic acid, having a molar ratio of magnesium tophosphonic acid of from 1:1 to 3:1.
 6. The method in accordance withclaim 5 wherein the molar ratio of magnesium to phosphonic acid is inthe range of from 1.9:1 to 2.8:1.
 7. The method in accordance withclaims 5 and 6 wherein the magnesium phosphonic acid salt is present ina level of from 2 to 300 parts per million (ppm).
 8. The method inaccordance with claim 7 wherein the magnesium phosphonic acid saltrepresents at least 70% by weight of the free-flowing solid composition.9. The method in accordance with claim 8 wherein the magnesiumphosphonic acid salt is present in a level of from 2 to 100 ppm.